This invention relates to an improved light lock and, more particularly, to a light lock that is especially suitable for effectively blocking light from entering a magazine, cassette or the like for photographic films.
Magazines, cassettes and the like for undeveloped photographic film commonly have light locks that are designed to exclude light from film in the magazine or cassette. One example of a light lock for a cartridge is found in U.S. Pat. No. 4,634,071, issued Jan. 6, 1987 in the name of H. E. Hertel and entitled "Light Tight Film Cartridge With Floating Light Seal". The seal of this patent comprises a pair of elongate sealing elements disposed adjacent opposite surfaces of a film strip. The sealing elements include a layer of black velvet-like light sealing material formed with a plurality of small, thin, flexible filaments closely spaced together and projecting outwardly into engagement with the film strip. Light locks of this kind rely on contact between the bristles of the sealing element and the film strip to exclude light from the interior of the magazine. Such contact increases wear on the bristles and encourages the bristles to break loose and adhere to the film.
U.S. Pat. No. 4,264,821, issued Apr. 28, 1981, in the name of W. Bauer, is directed to a cassette for an x-ray film. The cassette has a body part and a cover part that are hinged together so that the cassette can be opened to receive a sheet of x-ray film and closed to contain the sheet in a light tight manner. The cassette is provided with light seals around the edges comprising two parallel lips on one part of the cassette which receive a lip on the other part of the cassette when the cassette is closed.
Another x-ray film cassette is disclosed in U.S. Pat. No. 4,110,624, which issued on Aug. 29, 1978, in the name of A. P. Conteas. In this patent, a light trap has two parts formed of molded spongy, opaque plastic material comprising a female part of generally U-shaped configuration and a male part that fits within the female part and engages the bottom of the female part. The material forming the light trap also acts as a spring for a catch that holds the parts together and is effective to cause the catch to be retained in the closed position. Thus, there is a force urging the parts of the light trap away from each other.
Thus, in some of the prior art light locks, fibers of light lock elements are urged into contact with the film to effect the light lock. Others are void of fibers, and this may enable light to be reflected off the walls forming the light lock and ultimately find its way into the cassette to expose the film. Still others rely on compression of the parts forming the light lock which results in a force urging the parts of the light lock apart.